The present invention relates generally to the forming of an electromechanical cable and more particularly to a method and manufacture for forming an improved electromechanical cable of the type producing an antitorsional effect when subjected to flexion and tensile stresses such as are encountered during wind-up and deployment operations of the cable.
Conventionally, electromechanical cables employ one or more inner electrical conductors which may be individually insulated and are formed into a cable core by covering the conductors with a dielectric, e.g., an extruded plastic material. As is typical of this type of cable, the insulated core is provided with an outer armor for withstanding the flexion and tensile stresses, the armor being constituted by a rigid metallic tubular member enclosing the core or by a layer or layers of armor tapes wrapped spirally or helically around the dielectric of the core.
According to a known method, an armored cable of the kind under discussion, is formed by continuously moving a pair of flexible tape-shaped metallic armor members into contact with a continuously advanced cable core. Prior to engaging the cable core, the tape-shaped armor members are initially fed through a pair of forming dies and are performed into two identical concave-convex halves, each of which is substantially subjected to a crimping process in a crimping die. The cable core, in this instance, is composed of a plurality of disc-shaped insulating members spaced axially of the inner, electrically-conductive core members, the latter being individually insulated. The two armor halves are retained in position on the cable core by spirally wrapping layers of tarred insulating tape around the periphery of the armor members.
Another known electromechanical cable utilizes a cable core composed of the usual conductors covered with a foamed cellular polyolefin dielectric or a synthetic thermo-plastic insulating material. Helically wound yarns of a suitable jute are provided over the cable core and which, in turn, are covered with a metallic armoring of galvanized steel wires wound helically to hold the wires together and to ensure flexibility of the cable. To complete this cable structure, a covering of tarred insulating material is applied over the metallic wires.
When the layer of steel wires helically wound over the cable core, is subjected to substantial tensile stresses along the axis of the cable, a torque may result which causes rotation about the cable axis of all those transverse sections of the cable which are not linked.
Moreover, during laying or wind-up operations or suspension of the cable from an overhead structure to a lower structure in which condition the cable is alternately subjected to stretching and oscillating motions, temporary and unavoidable decrease in the longitudinal stress on the cable frequently results in warping and knotting of the cable which may eventually impart permanent electrical and/or mechanical damage thereto.
Furthermore, as a result of the rather rigid armor structures of typical, conventional cables and their generally inherent high mechanical resistance as regards flexibility, these prior art cable constructions are, on the whole, unsatisfactory as regards withstanding both flexion and tensile stresses, which are frequently very high, and which occur both during deployment and wind-up operations, the former involving, for example, deployment of the cable along a generally straight path parallel with the main axis of the roll from which the cable is fed.
Many attempts have been made to eliminate the above disadvantages by providing a highly flexible reinforced thermoplastic body incorporating embedded steel armoring strands and disposed or extruded around the cable core. So far, however, these attempts have failed to provide a practical solution by means of which the torsional reaction of the armoring is eliminated when the cable is subjected to flexion and tensile stresses encountered primarily during deployment operations.
Similarly, proposed reinforced structures which involved open weave or braided reinforcing cloth, or the like, laminated between sheets or layers of thermoplastics, or the like, failed to provide the desired result.